Steer by wire road vehicle steering system provided with a telescopic support element for the steering wheel

ABSTRACT

A steering system for a road vehicle; the steering system comprises: a steering wheel provided with an outer ring, which is mounted so as to rotate around a rotation axis and has no mechanical connection to steering wheels; a support element, which, on one side, can be rigidly fixed on the inside of the vehicle and, on the other side, is connected to the steering wheel so as to support the steering wheel; and a position sensor, which is designed to detect the angular position of the outer ring of the steering wheel around the rotation axis. The support element is telescopic so as to vary its axial size along the rotation axis in order to change the axial position of the steering wheel.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application claims priority from Italian Patent ApplicationNo. 102017000121876 filed on Oct. 26, 2017, the disclosure of which isincorporated by reference.

TECHNICAL FIELD

The invention relates to a “steer by wire” road vehicle steering system.

PRIOR ART

In a road vehicle, a steering system is provided, which fulfils thefunction of controlling the steering angle, namely the angle existingbetween the direction of the front wheels (i.e. the plane of rotation ofthe front wheels and the longitudinal axis of the road vehicle. Thesteering system comprises a control shaft, which is arranged crosswise,is mechanically connected, at its opposite ends, to the hubs of thefront wheels, and is mounted in an axially sliding manner in order tochange the steering angle. Furthermore, the steering system comprises asteering wheel, which is mounted in a rotary manner inside the passengercompartment and is mechanically connected to the control shaft by meansof a transmission device so that the rotation of the steering wheeldetermines an axial translation of the control shaft and, hence, acorresponding variation of the steering angle.

In the automotive industry there is a tendency towards an increasing useof “drive by wire” systems, in which the direct mechanical connectionbetween the controls of the vehicle (steering wheel, accelerator, brakeclutch, gear stick) and the actuators of the vehicle (steering tie rod,throttle valve, brake pump . . . ) is replaced by a (virtual) electronicconnection, which involves the use of a position sensor, which reads theposition of a control of the vehicle and communicates it to anelectronic control unit, which controls an (electric or hydraulic)motor, which operates the corresponding actuator of the vehicle.

In modern vehicles, “drive by wire” systems are regularly used tocontrol the accelerator as well as the gearbox controls and arecurrently spreading for the control of the brake and, in the nearfuture, they should also be implemented in relation to the control ofthe steering wheel. Patent applications WO2017115411A1, US2017158222A1,US2016068182A1, WO2017097662A1 describe “steer by wire” road vehiclesteering systems, i.e. systems with no mechanical connection between thesteering control (i.e. the steering wheel) and the steering tie rod.

Patent application DE102015224602A1 describes a steering system of aroad vehicle comprising a support element, which, on one side, can berigidly fixed on the inside of the vehicle and, on the other side, isconnected to a steering wheel so as to support the steering wheel; thesupport element is telescopic so as to vary its axial size along torotation axis of the steering wheel in order to change the axialposition of the steering wheel.

DESCRIPTION OF THE INVENTION

The object of the invention is to provide a “steer by wire” road vehiclesteering system, which can be manufactured in a simple and economicfashion and, at the same time, is compact, effective and efficient.

According to the invention, there is provided a “steer by wire” roadvehicle steering system according to the appended claims.

The appended claims describe preferred embodiments of the invention andform an integral part of the description.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described with reference to the accompanyingdrawings, showing a non-limiting embodiment thereof, wherein:

FIG. 1 is a schematic plan view of a road vehicle provided with a “steerby wire” steering system according to the invention;

FIG. 2 is a schematic, partially sectional view of a transmission deviceof the steering system of FIG. 1;

FIGS. 3-10 are schematic, partially sectional views of correspondingvariants of the transmission device shown in FIG. 2;

FIG. 11 is a perspective view of a mechanical limit stop device of thetransmission device shown in FIGS. 3, 6 and 9;

FIG. 12 is a side view of the limit stop mechanism of FIG. 11;

FIG. 13 is a side view, with a longitudinal section, of the limit stopmechanism of FIG. 11; and

FIG. 14 is a side view, with a longitudinal section, of a variant of thelimit stop mechanism of FIG. 11.

PREFERRED EMBODIMENTS OF THE INVENTION

In FIG. 1, number 1 indicates, as a whole, a road vehicle provided withtwo front steering wheels 2 and two rear drive wheels 3, which receivethe torque from a powertrain system.

The road vehicle 1 comprises a steering system 4, which fulfils thefunction of controlling the steering angle, namely the angle existingbetween the direction of the front wheels 2 (i.e. the plane of rotationof the front wheels 2) and the longitudinal axis of the road vehicle 1.

The steering system 4 comprises a steering mechanism 5, which can beoperated so as to change the steering angle, is arranged crosswise andconsists of a central rod, which can axially slide and is mechanicallyconnected to the fork ends of the front wheels 2 through articulated tierods. Furthermore, the steering system 4 comprises a steering wheel 6,which is mounted in a rotary manner inside a passenger compartment andis electronically (virtually) connected to the steering mechanism 5 bymeans of an electronic transmission device 7 (without mechanicalconnection) so that the rotation of the steering wheel 6 determines anaxial translation of the steering mechanism 5 and, hence, acorresponding variation of the steering angle. In other words, there isno mechanical connection between the steering mechanism 5 and thesteering wheel 6 and the transmission device 7 only creates a functional(not mechanical) connection between the steering mechanism 5 and thesteering wheel 6.

The transmission device 7 comprises a sensor 8, which detects in realtime the angular position of the steering wheel 6 and the torque appliedby the driver to the steering wheel 6; obviously, the sensor 8 iscapable of determining the angular position of the steering wheel 6 inan extremely safe manner by carrying out different independent andredundant reading operations aimed at reading the angular position ofthe steering wheel 6. It should be pointed out that the sensor 8 can bedirectly coupled, in a mechanical manner, to the steering wheel 6 or toany other part that is angularly integral to the steering wheel 6.

Furthermore, the transmission device 7 comprises an actuator device 9,which operates the steering mechanism 5 so as to control the steering ofthe front steering wheels 2 of the road vehicle 1 and comprises anelectric motor 10 and a transmission 11, which mechanically connects theelectric motor 10 to the steering mechanism 5. As already mentionedabove, the electric motor 10 (namely, the actuator device 9) ismechanically completely independent of and separate from the steeringwheel 6 and is designed to control the steering of the front steeringwheels 2 of the road vehicle 1 without any type of mechanicalforce/torque coming from the steering wheel 6.

Finally, the transmission device 7 comprises an electronic control unit(“ECU”) 12, which is connected to the position sensor 8 so as to receivethe reading of the angular position of the steering wheel 6 and isdesigned to control the electric motor 10 of the actuator device 9 so asto adjust the steering of the front steering wheels 2 of the roadvehicle 1 based on the angular position of the steering wheel 6. Thecontrol unit 12 can physically consist of one single device or ofdifferent devices separated from one another and communicating with oneanother through the CAN network of the road vehicle 1.

According to FIG. 2, the steering wheel 6 is mounted so as to rotatearound a rotation axis 13. According to a possible embodiment (shown byway of example in FIGS. 2-4 and 8-10), the entire steering wheel 6 (i.e.both the central hub 14 and an outer ring 15) is mounted so as to rotatearound the rotation axis 13; according to an alternative embodiment(shown by way of example in FIGS. 5-7), the central hub 14 of thesteering wheel 6 is fixed (i.e. it does not rotate around the rotationaxis 13), whereas the outer ring 15 of the steering wheel 6 is mountedso as to rotate around the rotation axis 13.

The transmission device 7 of the steering system 4 comprises an electricmotor 16, which is directly connected to the steering wheel 6 so as toapply a variable feedback torque to the steering wheel 6 (to the outerring 15 of the steering wheel 6); in other words, the function of theelectric motor 16 is that of applying to the steering wheel 6 (to theouter ring 15 of the steering wheel 6) a variable torque that transmitsto the driver torque sensations that are similar to the torquesensations of a traditional steering wheel mechanically connected to thesteering wheels. In the absence of the electric motor 16, the steeringwheel 6 (the outer ring 15 of the steering wheel 6) would rotate aroundthe rotation axis 13 always with the same type of effort, thuspreventing the driver from receiving any type of feedback from thesteering wheel 6 (in other words, the steering wheel 6 would behave likethe steering wheel of a video game instead of like the steering wheel ofthe an actual vehicle). The electric motor 16 comprises a stator 17,which does not rotate, and a rotor 18, which can rotate relative to thestator 17 around the rotation axis 13 (namely, is coaxial to thesteering wheel 6) and is mechanically connected to the steering wheel 6(to the outer ring 15 of the steering wheel 6) so as to apply a variablefeedback torque to the steering wheel 6. Furthermore, the electric motor16 supports the steering wheel 6, i.e. the steering wheel 6 is mountedon the electric motor 16; as a consequence, the steering wheel 6 (theouter ring 15 of the steering wheel 6) is rigidly integral to the rotor18 of the electric motor 16 and is supported by the rotor 18 of theelectric motor 16.

In the embodiment shown in FIGS. 2 and 3, in the electric motor 16, therotor 18 is internal and, therefore, it is radially arranged on theinside of the stator 17. In this embodiment, the rotor 18 of theelectric motor 16 comprises a shaft 19, which supports the steeringwheel 6; in particular, the bearings 20, which support the rotor 18 andare interposed between the rotor 18 and the stator 17, are preferablycoupled to the shaft 19 of the rotor 18.

In the alternative embodiment shown in FIGS. 4-8, in the electric motor16, the rotor 18 is external and, therefore, it is radially arranged onthe outside of the stator 17. In this embodiment, the rotor 18 of theelectric motor 16 generally (though, not necessarily) is without shaft.This embodiment is particularly advantageous when the central hub 14 ofthe steering wheel 6 is fixed (i.e. does not rotate around the rotationaxis 13) and the sole outer ring 15 of the steering wheel 6 can rotatearound the rotation axis 13; indeed, in this embodiment, the central hub14 of the steering wheel 6 can be directly connected to the stator 17 ofthe electric motor 16 (i.e. the central hub 14 of the steering wheel 6can be rigidly constrained to the stator 17 of the electric motor 16),whereas the outer ring 15 of the steering wheel 6 can be directlyconnected to the rotor 18 of the electric motor 16 (i.e. the outer ring15 of the steering wheel 6 can be rigidly constrained to the rotor 18 ofthe electric motor 16).

In all the embodiments shown in the accompanying figures, thetransmission device 7 of the steering system 4 comprises a supportelement 21, which, on one side can be rigidly fixed on the inside of theroad vehicle 1 (in particular, to the dashboard of the road vehicle 1)and, on the other side, is rigidly connected to the stator 17 of theelectric motor 16 so as to support the electric motor 16. In otherwords, the support element 21 is the mounting means through which theelectric motor 16 (and, hence, the steering wheel 6 supported by theelectric motor 16) is installed and fixed on board the road vehicle 1.

According to a preferred embodiment, the support element 21 istelescopic so as to vary its axial size along the rotation axis 13 inorder to change the axial position of the electric motor 16 and, hence,of the steering wheel 6. In particular, the support element 21 comprisesan outer tubular body 22, which can be rigidly fixed on the inside ofthe vehicle 1 and is internally hollow, namely has, on the inside, achamber 23, which is open on one side (facing the electric motor 16);furthermore, the support element 21 comprises an inner body 24, which isrigidly connected to the stator 17 of the electric motor 16 (i.e.supports the stator 17 of the electric motor 16), is partially arrangedinside the outer body 22 (i.e. in the chamber 23 of the outer body 22),and can axially slide relative to the outer body 22. It should bepointed out that the inner body 24 can only slide axially relative tothe outer body 22 and, therefore, cannot make any rotation relative tothe outer body 22.

In the embodiment shown in the accompanying figures, the outer body 22is provided with a bracket 25, which is used to fix the outer body 22(hence, the support element 21) to the dashboard of the road vehicle 1.

The support element 21 comprises an actuator device 26, which isarranged on the inside of the outer body 22 (i.e. is housed in thechamber 23 of the outer body 22) and is designed to axially translatethe inner body 24 relative to the outer body 22. The actuator device 26always has the function of stopping (forbidding) the axial translationbetween the two bodies 22 and 24, so as to make sure that, in use, thesteering wheel 6 remains still in a predefined axial position;furthermore, the actuator device 26 can be active, i.e. have an(electric) motor, which causes an axial translation movement of theinner body 24 relative to the outer body 22, or it can be passive, i.e.need the manual intervention of the driver in order to cause an axialtranslation movement of the inner body 24 relative to the outer body 22.In the non-limiting embodiments shown in the accompanying figures, theactuator device 26 is active and comprises an electric motor, which isintegral to the outer body 22 and causes the rotation of a worm screw,on which an abutment is screwed, which is integral to the inner body 24.

According to FIG. 7, the stator 17 of the electric motor 16 has, at thecentre, a cable-leading through duct 27, which is coaxial to therotation axis 13; similarly, the inner body 24 of the support element 21also has a cable-leading through duct 28, which is elbow-shaped (i.e.“L”-shaped) and has an opening, which is obtained through a base wall ofthe inner body 24, faces and is coaxial to the cable-leading duct 27,and another opposite opening, which is obtained through a side wall ofthe inner body 24. A cabling 29 (i.e. a set of electrical cables groupedtogether to form one single bundle) is provided, which originates fromthe central hub 14 of the steering wheel 6 and is arranged through thecable-leading ducts 27 and 28 so as to electrically connect the steeringwheel 6 to the rest of the road vehicle 1. In this embodiment, it ispossible to establish an electrical connection between the steeringwheel 6 and the rest of the road vehicle 1 without using rotary (i.e.sliding) electrical contacts or spiral cabling (which enables a certaindegree of twisting). The presence of the cable-leading duct 27 insidethe stator 17 of the electric motor 16 is particularly advantageouswhen, in the electric motor 16, the rotor 18 is external (according toFIG. 7), but it is also possible when, in the electric motor 16, therotor 18 is internal.

In the embodiments shown in FIGS. 2-8 and 10, the transmission device 7of the steering system 4 comprises the electric motor 16, which appliesthe feedback torque to the steering wheel 6; in the alternativeembodiment shown in FIG. 9, the transmission device 7 of the steeringsystem 4 has no electric motor 16 and, therefore, the steering wheel 6is directly connected to the inner body 24 of the support element 21; inparticular, there is a shaft that, on one side, is rigidly connected tothe steering wheel 6 and, on the opposite side, is connected to theinner body 24 of the support element 21 through bearings.

In the embodiments shown in FIGS. 2-9, the support element 21 is coaxialto the electric motor 16 and to the steering wheel 6; in the alternativeembodiment shown in FIG. 10, the support element 21 is not aligned withthe electric motor 16 and with the steering wheel 6 and is mounted lowerthan the electric motor 16 and the steering wheel 6; the lack ofalignment between the support element 21 and the electric motor 16 aswell as the steering wheel 6 increases the space available in the partof dashboard above the support element 21 (since the bracket 25 can beplaced lower), thus creating a larger space for information devices(control panel, screens) or other devices to be installed in the upperpart of the dashboard in front of the driver.

In the embodiments shown in FIGS. 3, 6 and 9, the transmission device 7of the steering system 4 comprises a mechanical limit stop device 30,which is coupled to the steering wheel 6 and limits, in both directions,the maximum angular width of the rotation of the steering wheel 6 aroundthe rotation axis 13, so that the steering wheel 6 can make, on thewhole, a rotation around the rotation axis 13 that is greater than 360°.It should be pointed out that the fact that the steering wheel 6 isallowed to rotate, on the whole, over more than 360° ensures (whendesired) a high steering “reduction”, namely in order to avoid (whendesired) a too direct steering (which is ideal when driving on a racetrack, but is not suitable for everyday driving in traffic). In theabsence of the mechanical limit stop device 30, it would be necessary tocreate “virtual” limit stops using the electric motor 16 to generate avery high braking torque, which simulates the presence of a mechanicallimits stop; however, this solution, despite being very elegant,requires an oversized electric motor 16 (in order to allow the electricmotor 16 to generate a braking torque that is high enough to stop therotation of the steering wheel 6) and, hence, leads to an increase insize, mass and costs.

According to FIGS. 11-14, the limit stop device 30 comprises a groove31, which is wound in a spiral around the rotation axis 13 over morethan 360° and has, at the two opposite ends, two abutments 32, whichdefine respective stop strikers; in other words, the groove 31 extendsin a spiral around the rotation axis 13 over more than 360° from anabutment 32 to the opposite abutment 32. By way of example, the groove31 could extend around the rotation axis 13 over approximately 720°(i.e. two complete rotations of the steering wheel 6) or overapproximately 1080° (i.e. three complete rotations of the steering wheel6). Furthermore, the limit stop device 30 comprises a pin 33, which isarranged inside the groove 31 so as to engage and follow the groove 31from an abutment 32 up to the opposite abutment 32; in other words, thepin 33 is inside the groove 31 and is forced to remain inside the groove31, thus covering the entire extension of the groove 31 from an abutment32 to the opposite abutment 32.

Furthermore, one between the groove 31 and the pin 33 is angularlyintegral to the steering wheel 6 (hence, rotates in an angularlyintegral manner with the steering wheel 6), whereas the other onebetween the groove 31 and the pin 33 is angularly integral to a partthat does not rotate together with the steering wheel 6 (in particular,is angularly integral to the inner body 24 of the support element 21).In other words, according to a possible embodiment, the groove 31 isangularly integral to the steering wheel 6, whereas the pin 33 isangularly integral to a part that does not rotate with the steeringwheel 6 (i.e. is angularly integral to the inner body 24 of the supportelement 21); alternatively, the pin 33 is angularly integral to thesteering wheel 6, whereas the groove 31 is angularly integral to a partthat does not rotate with the steering wheel 6 (i.e. is angularlyintegral to the inner body 24 of the support element 21).

Finally, one between the groove 31 and the pin 33 can axially sliderelative to the steering wheel 6. In other words, the groove 31 canaxially slide relative to the steering wheel 6 or the pin 33 can axiallyslide relative to the steering wheel 6.

In the embodiment shown in FIGS. 11, 12 and 13, the groove 31 isangularly integral to the steering wheel 6 (in particular, to a shaft 34coaxial to the rotation axis 13 which rigidly supports at least theouter ring 15 of the steering wheel 6) and can also axially sliderelative to the steering wheel 6 (in particular, relative to the shaft34); as a consequence, the pin 33 is rigidly connected to a part thatdoes not rotate with the steering wheel 6 (i.e. is angularly integral tothe inner body 24 of the support element 21). In this embodiment, thegroove 31 is coupled to the steering wheel 6 (in particular, to theshaft 34) through a splined coupling, which constrains in an angularmanner, enabling, at the same time, an axial sliding. It should bepointed out that the groove 31 can be mounted on any part that isangularly integral to the steering wheel 6 (i.e. that rotates around therotation axis 13 together with the steering wheel 6), for example theshaft 34 coaxial to the rotation axis 13 which rigidly supports at leastthe outer ring 15 of the steering wheel 6, the rotor 18 of the electricmotor 16 or the steering wheel 6 itself.

In the embodiment shown in FIG. 14, the groove 31 is angularly integralto the steering wheel 6 (in particular, to a shaft 34 coaxial to therotation axis 13 which rigidly supports at least the outer ring 15 ofthe steering wheel 6) and is also rigidly constrained to the steeringwheel 6 (in particular, to the shaft 34); as a consequence, the pin 33is angularly integral and can axially slide relative to a part that doesnot rotate with the steering wheel 6 (i.e. is angularly integral and canaxially slide relative to the inner body 24 of the support element 21).In other words, the pin 33 can axially slide, but cannot rotate relativeto a part that does not rotate together with the steering wheel 6 (i.e.relative to the inner body 24 of the support element 21).

The embodiments described herein can be combined with one another,without for this reason going beyond the scope of protection of theinvention.

The steering system 4 described above has numerous advantages.

First of all, the steering system 4 described above is particularlycompact, effective and efficient, since the total number of componentsof the transmission device 7 is reduced to a minimum. In particular, thesteering wheel 6 is directly supported by the electric motor 16, which,hence, applies the feedback torque to the steering wheel 6 withoutintermediate elements. Furthermore, the support element 21 is extremelysimple, functional and compact, as it has a tubular shape housing, onthe inside, the actuator device 26, which regulates the axial movementsof the steering wheel 6.

Moreover, the support element 21 allows the steering wheel 6 to cover amuch wider axial stroke, which can get up to 250 mm, without particularconstructive complications (also thanks to the absence of a connectionshaft towards the steering mechanism 5).

LIST OF THE REFERENCE NUMBERS OF THE FIGURES

-   -   1 road vehicle    -   2 front wheels    -   3 rear wheels    -   4 steering system    -   5 steering mechanism    -   6 steering wheel    -   7 transmission device    -   8 sensor    -   9 actuator device    -   10 electric motor    -   11 transmission    -   12 control unit    -   13 rotation axis    -   14 central hub    -   15 outer ring    -   16 electric motor    -   17 stator    -   18 rotor    -   19 shaft    -   20 bearings    -   21 support element    -   22 outer body    -   23 chamber    -   24 inner body    -   25 bracket    -   26 actuator device    -   27 cable-leading duct    -   28 cable-leading duct    -   29 cabling    -   30 limit stop device    -   31 groove    -   32 abutment    -   33 pin    -   34 shaft

1) A steering system (4) for a road vehicle (1); the steering system (4)comprises: a steering wheel (6) provided with an outer ring (15), whichis mounted so as to rotate around a rotation axis (13) and has noconnection to steering wheels (2); a support element (21), which, on oneside, can be rigidly fixed on the inside of the vehicle (1) and, on theother side, is connected to the steering wheel (6) so as to support thesteering wheel (6); and a position sensor (8), which is designed todetect the angular position of the outer ring (15) of the steering wheel(6) around the rotation axis (13); wherein the support element (21) istelescopic so as to vary its axial size along the rotation axis (13) inorder to change the axial position of the steering wheel (6); whereinthe support element (21) comprises: an outer body (22), which can berigidly fixed on the inside of the vehicle (1) and is internally hollow;an inner body (24), which is connected to the steering wheel (6), ispartially arranged on the inside of the outer body (22), and can axiallyslide relative to the outer body (22); and an actuator device (26),which is designed to axially translate the inner body (24) relative tothe outer body (22); and wherein the actuator device (26) is arranged onthe inside of the outer body (22). 2) The steering system (4) accordingto claim 1, wherein the outer body (22) is tubular and has, on theinside, a chamber (23), which is open on one side, partially houses theinner body (24) in an axially sliding manner, and houses the actuatordevice (26). 3) The steering system (4) according to claim 1, whereinthe actuator device (26) is designed to stop the axial translationbetween the outer body (22) and the inner body (24) so as to make surethat, in use, the steering wheel (6) remains still in a predefined axialposition. 4) The steering system (4) according to claim 1, wherein theactuator device (26) is active and comprises a first electric motor,which causes an axial translation movement of the inner body (24)relative to the outer body (22). 5) The steering system (4) according toclaim 4, wherein the actuator device (26) comprises: the first electricmotor, which is integral to the outer body (22); a worm screw, which iscaused to rotate by the first electric motor; and an abutment, which isscrewed in the worm screw and is integral to the inner body (24). 6) Thesteering system (4) according to claim 1, wherein the support element(21) is not aligned with the steering wheel (6) and is arranged lowerthan the steering wheel (6). 7) The steering system (4) according toclaim 1 and comprising a second electric motor (16), which applies avariable feedback torque to the outer ring (15) of the steering wheel(6), is interposed between the support element (21) and the steeringwheel (6) so as to support the steering wheel (6), and comprises astator (17), which is rigidly connected to the support element (21), anda rotor (18), which is rigidly connected at least to the outer ring (15)of the steering wheel (6). 8) The steering system (4) according to claim1 and comprising a third electric motor (10), which is mechanicallycompletely independent of and separate from the steering wheel (6) andis designed to control the steering of the steering wheels (2) of thevehicle (1). 9) The steering system (4) according to claim 8 andcomprising a control unit (12), which is connected to the positionsensor (8) so as to receive the reading of the angular position of thesteering wheel (6) and is designed to control the third electric motor(10) so as to adjust the steering of the steering wheels (2) of thevehicle (1) based on the angular position of the steering wheel (6). 10)The steering system (4) according to claim 1 and comprising a mechanicallimit stop device (30), which is coupled to the outer ring (15) of thesteering wheel (6) and limits, in both directions, the maximum angularwidth of the rotation of the steering wheel (6) around the rotation axis(13), so that the steering wheel (6) can make, on the whole, a rotationaround the rotation axis (13) that is greater than 360°. 11) Thesteering system (4) according to claim 10, wherein: the limit stopdevice (30) comprises a groove (31), which is wound in a spiral shapearound the rotation axis (13) over more than 360° and has, at the twoopposite ends, two abutments (32), which define respective stopstrikers; the limit stop device (30) comprises a pin (33), which isarranged on the inside of the groove (31) so as to engage and follow thegroove (31) from an abutment (32) to the opposite abutment (32); onebetween the groove (31) and the pin (33) is angularly integral to theouter ring (15) of the steering wheel (6), whereas the other one betweenthe groove (31) and the pin (33) is angularly integral to a part thatdoes not rotate together with the outer ring (15) of the steering wheel(6); and one between the groove (31) and the pin (33) can axially sliderelative to the outer ring (15) of the steering wheel (6). 12) Thesteering system (4) according to claim 11, wherein: the groove (31) isangularly integral to the outer ring (15) of the steering wheel (6) andcan axially slide relative to the outer ring (15) of the steering wheel(6); and the pin (33) is rigidly connected to a part that does notrotate together with the steering wheel (6). 13) The steering system (4)according to claim 12, wherein the groove (31) is coupled to thesteering wheel (6) through a splined coupling.